h265 has better compression but it's not easier to encode or decode, so performance wise it may be worse.
files will be smaller with h265.
Some new video cards and cpu's have dedicated hardware h265 support to speed things up.

Unity Technologies

As mentioned by @Lars-Steenhoff, the H.265's performance is tightly linked to its hardware decoder implementation.
Note that where hardware support is not provided, a software fallback implementation might be available, but, obviously, provides less than ideal decoding performance results.
The major gain of the H.265 codec is to offer similar video quality as the H.264 codec with approximately half the bitrate.
It aims to reduce storage space and bandwidth use.

That being said, I'm curious to see the results you get when updating your projects.

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